Go to Wal-Mart, Autozone, whatever and in the air freshener isle there is this stuff that comes in a can and actually kills bacteria (kinda like lysol for your car). You can drill a small hole in one of the AC evap containers under the glovebox and inject the stuff in there, then plug the hole. I had a funky smell for a while but one of the small cans of the stuff got rid of it, and its been fine ever since (although it will smell pretty strong the first couple of times you use the AC). There was a post on it a year or so back when Dayle had some new odor eater stuff that did the same thing, try a search.
But if there really is something dead up in there, you might want to take care of that first
